Be vigilant during your beach outings this summer, in the departments concerned. Something invisible to the naked eye could have slipped between your toes. This microalga called Ostreopsis poses a risk to swimmers. As proof, since 2021, their proliferation has continued to grow and has caused 900 poisonings on the Basque coast.

Flu-like symptoms, skin irritations, gastric disorders… The health effects are mild, but serious for people with respiratory problems, according to the National Health Security Agency (ANSES). ANSES warns as summer approaches, it is more urgent than ever to know how to spot it and set up monitoring, even beyond the Basque Country.

Because of the toxins it produces, Ostreopsis is the cause of poisoning causing coughing and breathing difficulties similar to the symptoms of flu. The signs of intoxication appear a few hours after contact with the microalgae. Fortunately, the symptoms will go away on their own after a few days. If you suffer from respiratory problems such as asthma, then it is recommended that you consult a medical professional or go to the hospital to be on the safe side.

Since Ostreopsis is a new phenomenon, citizens do not necessarily have the means to be alerted. ANSES published its opinion on Tuesday June 20, 2023, to speed things up as summer approaches. In this note, ANSES recommends adapting the frequency of health checks of bathing water. For the moment, the agency has established a grid with four levels of vigilance. This grid is made available to local authorities, in particular Regional Health Agencies (ARS).

There is no huge fear to have however, because it is from level 3 that things become serious for the citizen. An information message is made available (for example, a poster near the beaches). At level 4, the beaches concerned may possibly be closed by decision of the town hall.

Discover in our slideshow below which departments were affected by this toxic algae during the summer of 2023.